The four specific aims are to [1] elucidate the cellular biology of Ts1 and LRP by identifying structural domains of Ts1 that define LRP recognition, [2] define the structural determinants of Ts1 which allow RAP to regulate by LRP, [3] elucidate the mechanisms by which RAP regulates activity of LRP within the cell, and [4] define routes of intercellular trafficking of both LRP and RAP. These studies will have broad implications for understanding the normal and pathophysiological alterations which occur in developing vasculature.